1. Field of the Invention
The present invention relates to a PCM recording and reproducing apparatus in which analog audio information is recorded in digital form on a recording medium, i.e. a video tape of video tape recorder and a reproduced digital signal is reconverted to the original analog signal, and more particularly to a tape searching device for enabling the rapid search of a desired tape position.
2. Description of the Prior Art
As a tape searching device for a video tape recorder, a method could be proposed to extract for example, vertical synchronizing signals from a reproduced video synchronizing signal and count the number of those signals. However, those vertical synchronizing signals are mere pitch signals appearing at each predetermined length of a tape and they are not address signals for the tape. Accordingly, when a desired position of the tape is to be searched after a certain length of tape has been wound, the tape has to be first rewound to an initial position and then the vertical synchronizing signals are counted while the tape is wound forwardly. Therefore, the search operation is troublesome, and a long search time is required.
Another method could also be proposed in a PCM recording and reproducing apparatus to record and reproduce a digital signal which is a digital version of an analog audio signal, as well as digital address signals as addressing signals. This method, however, also has a disadvantage in that it cannot permit quick search as will be described below.
In the PCM recording and reproducing apparatus, a PCM signal format is in accord with a standard television signal such that the audio digital signals are accommodated in predetermined horizontal scan periods (e.g. 245 horizontal scan periods or 245 H) of one field (262.5 H) and the system control signals such as the address signals and content indexing signals are accommodated in another horizontal scan period (e.g. in one horizontal scan period preceding to the audio digital signals accommodating periods). In a helical scan type video tape recorder, those audio digital signals and address signals are recorded on the video tracks 2 of a magnetic tape 1 shown in FIG. 1, in which numeral 3 denotes an audio track of the tape 1 when it is to be used for video recording instead of PCM audio recording and numeral 4 denotes a control track. An arrow A indicates the direction of tape travel and an arrow B indicates the direction of rotation of a video head.
Referring to FIGS. 2 and 3, the movement of the magnetic tape 1 is explained. FIGS. 2 and 3 show top views of a rotary head and associated devices of the video tape recorder, in which FIG. 2 shows a normal playback condition while FIG. 3 shows fast-forward or rewind condition. In the normal playback condition, as shown in FIG. 2, the magnetic tape 1 is in contact with a pair of rotary heads 5a and 5b disposed on a disk 5 and an audio/control head 6, so that the video tracks 2 are played back by the rotary heads 5a and 5b while the audio track 3 and the control track 4 are played back by the audio/control head 6. Numeral 7 denotes a supplying impedance roller, numeral 8 denotes the guide poles and numeral 9 denotes a take-up impedance roller. During the fast-forward or rewind condition, the tape 1 is half-loaded as shown in FIG. 3 in order to assure smooth and high speed movement of the magnetic tape 1 and to protect the magnetic tape 1. Under these conditions, the video tracks 2 are not played back by rotary heads 5a and 5b but only the audio track 3 and the control track 4 are played back by audio/control head 6. As a result, during the fast-forward or rewind conditions which are necessary for the rapid search, the address signals recorded by the rotary heads 5a and 5b are not played back. Accordingly, the tape search operation has to be carried out in the normal speed playback condition and hence rapid search operation cannot be attained.